This is Thomas Mayer's blog about vacuum tube audio, to share updates about new amplifiers and preamplifiers and ELROG vacuum tubes.

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Thursday, June 26, 2014

Differential 10Y Line Preamp, Part 1

Hi!

I am often asked when I will finally present a push pull amplifier. In fact I am often perceived as being prejudiced pro Single Ended. While I do like the sound of my single ended designs, I am by no means religiously bound to this concept. In fact I did build push pull amplifiers in the past and probably will do so in the future. At the latest when somebody orders a push pull amplifier from me.

Such has happened for a preamplifier. A user of my 10Y line stage asked me for possibilities to upgrade it. So I proposed a differential version of it.

Differential in this case means that it will be a self balancing circuit. The beauty of such a concept is the possibility to build it without any capacitor in the signal path. And that's how this line stage will be done. Lot's of iron, no capacitors in the signal section. Everything decoupled from the power supply. Of course that means that 2 10Y tubes will be needed per channel. 4 of them in total. This is the top metal plate of the signal section:

The left half will be occupied by filament chokes. For the 4 sockets to fit, I had to use some different ones as usual, which have a smaller footprint. These allow the vibration damped sub assemblies to be narrower.

I often get emails about my technique of vibration damped sub assemblies for the tube sockets. So I will show this a bit more in detail in this first part. These are the basic elements used for that:

A rubber cylinder with metal threads at both ends. Threaded metal blocks get attached at either end.

The small metal plates which carry the tube sockets have threaded holes on the bottom:

Tube socket mounted:

Then the metal blocks get attached to the plate with screws:

The rubber elements screw into the sides of these metal blocks:

The small wire is there to make an electrical connection from the sub plate to the main plate. Another set of the metal blocks goes onto the other side of the rubber pieces: